A/C Thermostat Problem

I wasn't sure if I should put this in the electrical section or here since I think it's a wiring problem.

When I moved into my townhouse I found that the thermostat for the A/C and Heat didn't really work and it would continue to produce cold air or heat after it reached the target temperature. I bought a new digital theromostat thinking that the old one's guage was busted and since it was ancient it wouldn't be worth trying to fix. I installed the new one following the wiring diagram in the instructions, which happened to match the color coding of the old thermostat (I wrote down what colors went where just incase I needed to hook the old one up again). Anyways, it still doesn't work so I'm wondering if this is a wiring problem that is somewhere beyond the thermostat itself, or if the wire colors are wrong in my house.

Anyone have ideas for how I can tell what the problem is? If I need to call in a pro should I call an electician or an A/C company?

Thanks,
Keith

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A/C Thermostat Problem

Hi therumblefish

Not exactly sure how to answer. When you changed out the thermostat did it perform the same as the old one? The other question I would have to ask is what kind of equipment are you dealing with. If any of this is hard to answer, call in the proffesionals.

Good luck
Rusty

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A/C Thermostat Problem

The new thermostat does the exact same thing as the old one. The digital temperature guage reads accurately, but it doesn't actually control the A/C turning on or off. If I leave the air on all night long it will be freezing cold in the morning and the guage will tell me the right temperature. It just runs constantly for as long as you leave it set to "auto". I set the target temperature to 70 and when the actual temperature hits 70 it just keeps right on blowing cold air.

The old thermostat was the generic 1980's cheapo type, the new one is by Ritetemp. The A/C handler upstairs is by Goodman, and the outside unit is by the same company.

A/C Thermostat Problem

Hi again therumblefish

When you say it is in auto, are you talking about the mode switch (heat off cool auto) or the fan switch (auto / on). It sounds like your thermostat either way may be working properly. What may be going on is the unit is either undersized or has improper air flow. To decide this you will need to do an experiment. the first thing you need to do is set it to the appropriate mode rather it be heat or cool. Set fan switch into auto mode, turn system on let it run for a few minutes and let temperatures stabalize. This will usually take about 10 minutes of run time. If the mode you are using is the cooling mode, turn the thermostat temperature setting two degrees higher than the room temperature. If the unit shuts off you will know that the thermostat is ok. At this point if thermostat is functioning properly you will need to have a professional find out why system is not performing properly. If you chose the heating mode just do the reverse by letting room stabalize, turn thermostat two degrees cooler than the room temperature, if unit shuts off the same applies. If unit is new you may want to go back to the original installer and find out what was done. By all means get a second opinion, the original installer may know of a problem they dont want to devulge, your second opinion will be unbiased.

A/C Thermostat Problem

When I said auto I was referring to the mode switch (heat - off - auto - cool).

I had done a similar little experiment before but I went ahead and did exactly what you suggested. I pushed the reset button on the thermostat. The a/c had been off all afternoon and the temperature in the house was 75 so I set the target temperature to 72 and turned it to auto. The a/c immediately kicked on. When it hit 72 it should have turned off but it kept right on going and now it's 70 degrees.

The new thermostat is wired exactly as the original one and the a/c units are the original ones that were installed when the house was built in 1985.

I'm pretty positive it has to be some sort of electrical wiring problem somewhere and I do have a little bit of electrical experience, but not enough to know what wires it would be. I think I'll probably have to call a professional but I'm not sure if I should call an A/C company or a regular electrician.

Thanks for all your help so far, I appreciate you taking the time to reply.

A/C Thermostat Problem

Hi therumblefish

What you just said there helped a ton, I am going to give you the nomenclature for the thermostat and I think you can solve this. I have never heard of a right temp, but a thermostat is a thermostat.
RC= 24 volts hot A/C, usually red wire
RH= 24 volts hot Heat Mode, jumper to RC
G= Fan or blower, usually green wire
Y= A/C contactor, usually yellow wire
W= Heat, usually white
C= Common 24 volts neutral. MUST GO TO FURNACE COMMON. ,usually blue.
If wiring is correct the next experemint you need to do is slightly more complicated, but you changed out stat you can do this. It does not sound like you have a high voltage wiring problem, it is in your low voltage or 24 volt circuit. This is the voltage that the thermostat operates at. Use the wiring color code I gave you and check it against your furnace and thermostat. If everything is ok there, Remove the wiring from the thermostat. This is going to sound scary but don't let it intimidate you. Take the red wire and connect it with the green wire, the furnace blower should come on. Seperate them and within 1 1/2 minutes the blower should shut off. If all that functions connect the green red and yellow together, there will be a little spark, its ok. Then seperate them and make sure everything shuts down. If that happens, you have a thermostat that is not working properly. The thermostat may have a dip switch that is not in the proper position or may need to be configured. Counsult your installation manual that came with the thermostat. Once you have done all this, If thermostat is bad return it and get your money back. I am not sure if you have them available, but if so I would have to reccomend a White Rodgers 80 series. They are amongst the most reliable and the most user friendly available. Good luck and don't get discouraged. I will help you as much as you need.

A/C Thermostat Problem

Thanks again so much for your help. It will probably be a day or two before I can find the time to take it apart since I work and go to school. When I've done what you said I'll reply with the results so that you know what happened.